1. Field of the Invention
The invention relates to a method for producing photographic copies from photographic originals.
2. State of the Art
Typically, photographic copies of photographic originals are produced by photographic copiers (printers), in which the originals are exposed to copying light and projected onto photographic copy material. Very often in the industry, the original material is exposed negative film strips, which contain frames acting as originals, and in which the copy material is photographic paper, or photo paper, on which the paper prints are produced in the form of photographic copies. For the sake of simplicity, this situation will therefore be addressed as an example; that is, the negative films or the frames on them stand as a representative example of original material or originals, and the photo paper or the paper prints are a representative example of photographic copy material or photographic copies. Naturally, slides can also serve as originals, and sheets can serve as photographic copies.
Customers who turn in their exposed negative films so that paper prints can be made from them increasingly expect ever shorter processing times for their orders while requiring high quality of the paper prints. Today, in large photo processing laboratories, high-speed printers that are designed for very high throughput rates are used to make the photographic copies. To assure the most efficient, interruption-free operation and hence the most optimal possible utilization of capacity and economical operation of the printer, the individual negative film strips are typically delivered to the high-speed printer in the form of a length of film spliced together. To that end, a large number of negative film strips are spliced into one long, cohesive length of film which is wound up into a roll. From such a roll, the length of film is then fed into the copier--that is, the printer--where the projection of the frames onto the still unexposed photo paper takes place, the photo paper typically being delivered to the printer in the form of a length of paper. The length of film is subsequently cut into short strips--typically with four frames each. The exposed length of photo paper is developed in a copy material processor, for example a paper processor, and the individual paper prints on the length of photo paper are cut apart. Finally, the negative film strips and the associated paper prints are collated order by order and placed in envelopes.
In photographic copiers (printers), it is normally not possible to use standardized, uniform quantities of copying light; instead, exposure control processes are employed, in which the most optimal quantities of copying light, and in particular the exposure times for the three basic colors of blue, green, red are determined for the individual frames. Both the specific properties of the copy material (photo paper) and the film-specific properties and the properties of the frame must all be taken into account. Such exposure control processes are disclosed in European Patent Disclosures EP-A 0 475 897 and EP-A 0 586 773.
In such exposure control processes, the individual frames of the negative films are analyzed. The analysis is performed, initially by regional scanning (for example, pixel by pixel), of the frame of the negative film to be copied with the aid of scanning light in a scanning station of the printer. The scanning light transmitted or remitted from each scanned region of a frame of the negative film is delivered to a detector array, broken down spectrally, and converted into wavelength- and intensity-dependent electrical scanning signals. The electrical scanning signals are then digitized, and with the aid of these signals, frame-specific data are ascertained. With the aid of the data obtained, the requisite quantities of copying light are then ascertained.
To enable the quantities of copying light required in the various colors of blue, green and red to be ascertained correctly, the reaction of a particular photo paper to changes in the respective colors of the copying light must be known (i.e. how the paper density varies over the concentration of the pigments of yellow, magenta, and cyan as a function of a change in the copying light in the colors blue, green and red). Thus a model for the photo paper--a paper model--must be known, which is representative for the absorption properties of the photo paper in the event of a change in the exposure. Naturally, this paper model also has to take into account the secondary absorptions of the photo paper. Secondary absorption means that when light of one color, such as blue, acts upon the photo paper, a change in the optical density of the photo paper in all three colors results.
A model must also be known for how the photo paper reacts to changes in the spectral film density of the negative film in order to determine how the copying light (exposure) has to be changed to compensate for deviations in the actually measured density of a negative from the average film density (that is, a deviation from the "norm"). Since, to that end, the film must be viewed with the "eyes of the photo paper", this is a paper-related film model.
If both models, namely the paper model and the paper-related model, are adequately well known and optimized, then the printer is setup-tested. As a rule, it is now possible to predict what change in the copying light in the particular color of blue, green or red is necessary in order to achieve a certain change in the paper density in the colors yellow, magenta and cyan. Thus, once a printer has been setup-tested using the ascertained data for the particular frame, the quantities of copying light required for the projection can be determined. Based on these quantities of copying light, corresponding control signals are ascertained for color filters provided in the copying station of the printer. These filters are placed in the copying beam path in accordance with the control signals when the negative frame is copied onto the photo paper. Once the negative frame has been copied onto the photo paper, the copies made in this way are developed in a developing station which may be an integral component of the printer.
Although such exposure control processes are very powerful and have stood the test of time, it often happens that the copies made in a first pass may not meet the customer's high demands for picture quality. The paper prints produced in a first pass are typically inspected, and the operators determine correction values for the paper prints that are not satisfactory. The originals corresponding to the unsatisfactory copies are copied again in a second pass, taking into account the determined correction values. As a rule, the operators input these correction values manually, for instance via a keyboard, into the computing and control unit of the printer.
For the second pass, a plurality of fundamentally different methods and procedures are known. One method is the use of the same printer for the second pass to produce the corrected copies of the first pass. Two basic variants of this can be distinguished.
In the first variant, the entire length of film spliced together on a roll is rewound, after the first pass, onto a roll on the output side of the printer; that is, the length of film is not cut apart. This roll is then docked to the input side of the printer, and the entire length of film is sent through the printer once again. In the second pass, however, only those frames that produced unsatisfactory copies in the first pass are projected onto the photo paper; the other frames pass through the printer without being projected again.
In the second variant, the length of film is cut apart into short strips--typically with four frames each--after the first pass, and the strips that contain frames that produced unsatisfactory copies in the first pass are separated out and spliced together again and collected, for instance on a roll. This roll is then docked to the input side of the printer, and the second pass is performed.
In both variants, during the second pass, the frames that produced unsatisfactory copies in the first pass are rescanned in the scanning station of the printer and analyzed. In the ensuing determination of the quantities of copying light, the correction values determined by the operators after the first pass are taken into account. However, the problem then arises that the frame-specific data (without taking the correction values into account) determined in the second pass can deviate from those data determined for the same frame in the first pass. There are various reasons for this. For instance, the originals in the second pass in the scanning station may have shifted slightly in position compared with the first pass, so that the scanned regions of the original in the second pass are not completely identical to those of the first pass. As a result it is possible that the exposure values determined in the second pass may deviate from those determined in the first pass, even without considering the correction values but only because of the slightly shifted scanned regions.
Another reason arises particularly in the aforementioned second variant, in which the short negative strips are re-spliced together after the first pass. It is a known method that before a frame is projected, a relatively large number of frames, for instance all those in one negative film, are first scanned in the scanning station, and film-specific data resulting from the scanning of a plurality of frames are utilized to calculate the exposure. If in the second pass the individual short negative strips, each containing four frames and generally making up only a fraction of the original negative film, are now spliced together, once again this can mean that in the second pass, even without taking into account the correction values, quantities of copying light can be determined that differ from those of the first pass.
Since the quantities of copying light determined in the first and second passes for an individual frame can differ even before taking the correction values into account, taking the correction values into account in the second pass does not lead to the desired improvement in picture quality. Under this scenario, still another copying procedure must be performed. This situation is highly undesirable from the standpoint of economical and efficient operation of the printer.
To solve this problem it has been proposed that in the first pass, certain exposure values be stored in memory and reused in the second pass. Consequently, in the second pass the frame-specific data are not redetermined entirely. Instead, the exposure values of the first pass are used together with the correction values determined in order to determine the quantities of copying light for the second pass. But even this method has various disadvantages. In particular, it does not facilitate the optimal utilization of the printer's capacity. Modern high-speed printers used in large photoprocessing laboratories are technologically very complex, extremely powerful machines, in which high-quality components are used. It is understood that such machines are relatively costly, and it is therefore desirable that their capabilities and capacities be utilized as optimally as possible, to assure economical and efficient operation. However, if one performs the second pass as well on such a high-speed printer, this is not making optimal use of such a printer, because in the second pass, not every frame is projected but only those that produced unsatisfactory copies in the first pass. When the exposure values of the first pass are used for the second pass, the scanning station, which is designed to be of very high quality, is practically unused. Moreover, in the case where the short negative strips have to be re-spliced after the first pass, a large number of such short negative strips with frames not correctly exposed in the first pass have to be collected together to makeup a roll that is sufficiently large to make it worthwhile to process it using the high-speed printer in the second pass. Yet the waiting time needed for collecting these strips can cause delays and can slow down the total processing time for a customer order.
These are the reasons for the changeover in many large processing laboratories so that the first pass is done on a high-speed printer, while the necessary corrections are made using another printer. The second pass and possibly every further printing pass is normally done with a printer, such as a minilab, that is less powerful and is designed for lesser throughputs. But even this method is still in need of improvement because the first pass data--if they are available at all or can be transferred to the second printer--are of only very limited use for the second pass, since identical exposure values, such as exposure times, normally do not lead to identical copies on both the high-speed printer and the second printer. The two printers have different exposure systems, such as different copying light sources and/or different color filters. As a rule, the frames or originals in the second printer must be rescanned to determine the quantities of copying light, which has the disadvantages already described above. If one were to perform the second pass in the second printer using the same exposure times that were used in the first printer to make the first copies, then the second copies, despite the same exposure times, would differ from the first copies. It is clear that efficient, targeted correction in the second pass can be accomplished only with great difficulty. Since the first pass data can hardly be used in such a method, there is also a need for improvement in the second method using two printers.